Generally, a power plug is connected with a load device through a power supply line and is inserted into a receptacle connecting to a power source. The power plug includes plural prongs inserted into the receptacle and a casing for protecting the prongs.
In the conventional power plug, because the plural prongs are fixed to the casing, an insertion direction of the plug is fixed (in insertion of the prongs into the receptacle). When plural plugs are inserted into the same receptacle, because the plural plugs and power supply lines thereof are interfered with each other, it is inconvenient to insert and pull out the plus into/from the receptacle. And, the power supply lines may be twisted with each other according to positions of the receptacle and load devices.
In addition, in order to cut off power applied to a load device, prongs have to be pull out from the receptacle, it is inconvenient to use.
In particular, because it is intricate to separate/connect the power plug from/to the receptacle, a user may turn off only power of the load device without pulling out the power plug from the receptacle, in that case, power is wasted, a life span of the load device is reduced, and fire may occur due to overload.
In order to solve the above-mentioned problems, a rotational plug is disclosed in Korea Practical New Device No. 87-5892. In the rotational plug, an intermediate rotational plate connected to a power supply line is installed at a plug body having prongs, the intermediate rotational plate and the plug body are connected to a power source through an electric conduction plate, a plate spring is interposed between the intermediate rotational plate and an upper rotational plate installed at the upper portion of the plug body in order to ground the electric conduction plate with the plug body.
In the rotational plug, the plug body and the intermediate rotational plate connecting to the power supply line are respectively rotated.
However, in the rotational plug, because the intermediate rotational plate is rotationally combined with the plug body, a position of the power supply line can be varied. However, because the electric conduction plate is always contacted to the plug body, it is impossible to perform power on/off function, in order to turn off power, the user has to pull out the plug from the receptacle, and accordingly it is inconvenient to use.
And, a plug disclosed in Korea Practical New Device Official Report No. 93-22426 includes a fixed member at which an upper and a lower contact terminal are fixed; and a rotational member elastically contacting to a certain side of the fixed member at which a power supply line is fixed. In that plug, although the power supply line is moved at various angles in the rotation of the rotational member, power applied to the upper and lower contact terminals can continually flow through the power supply line.
However, in the plug, the position of the power supply line can be changed by the respective rotation of the rotational member at which the power supply line is fixed, however, there is also no power cut off function, in order to cut off power the user has to pull out the plug from the receptacle, and accordingly it is inconvenient to use.
In order to solve the above-mentioned problem, an electrical plug disclosed in Korea Practical New Device Official Report No. 93-22426 had a power on/off function for turning on/off power applied to a load device.
In more detail, the power plug includes an external power input unit inserted into a receptacle so as to receive an external power source; a power control unit having a power supply/cut off unit made of a conductive material to supply/cut off the external power from the external power input unit to an electric appliance; and a power display unit for displaying the power supply/cut off state.
However, in the plug, when the plug is inserted into the receptacle, it is possible to turn on/off power supplied to the load device by rotating the power control unit. However, the power control unit may be easily rotated by an external force, an adjusted position set by the rotation of the rotation control unit may not be maintained stably.
As mentioned above, when the rotation control unit is rotated by the external force, because it is impossible to maintain the power on/off state, power applied to the load device may be abruptly cut off, and accordingly the load device may be damaged by that.
Besides, a plug disclosed in Japan Practical New Device Official Report No. Pyung6-58585 and a rotational plug disclosed in Korea Practical New Device Official Report No. 99-17451 respectively have a system changable a position of a power supply line by using a rotational plug, however, they also had the above-mentioned problems.